Assembly tool

ABSTRACT

An instrument for assembling an implant on a neck. The implant and neck being coupled via a taper having a taper axis. The instrument includes a frame having a distal portion and a proximal portion, the distal portion of the frame including a retaining member adapted to engage a portion of the neck. The retaining member includes a bracket extending from the distal portion of the frame, the bracket adapted to engage opposing sides of the neck. The instrument also includes a force applier retained in the proximal portion of the frame. The force applier includes a screw having a screw axis that is coaxial with the taper axis, wherein the screw is adapted to engage the implant. As the screw is turned, the force applier applies a force on the implant while the neck is held in place by the frame, thereby causing the tapers of the implant and neck to engage.

This application claims priority under 35 U.S.C. §119 to U.S. PatentApp. Ser. No. 62/103,611 entitled “ASSEMBLY TOOL” which was filed Jan.15, 2015 and is expressly incorporated herein by reference.

CROSS-REFERENCE TO RELATED APPLICATION

Cross-reference is made to U.S. Patent App. Ser. No. 62/103,826 entitled“FEMORAL STEM INCLUDING AN ANCHOR TO FACILITATE ASSEMBLY ANDIMPLANTATION,” which was filed Jan. 15, 2015 and is expresslyincorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to the field of orthopedics,and, more particularly, to an instrument for assembling a head to astem.

BACKGROUND

A joint within the human body forms a juncture between two or more bonesor other skeletal parts. The ankle, hip, knee, shoulder, elbow and wristare just a few examples of the multitude of joints found within thebody. As should be apparent from the above list of examples of joints,many of the joints permit relative motion between the bones. Forexample, the ankle permits a hinge movement, the knee allows for acombination of gliding and hinge movements and the shoulder and hippermit movement through a ball and socket arrangement.

The joints in the body are stressed or can be damaged in a variety ofways. Gradual wear and tear is imposed on the joints through thecontinuous use of a joint over the years. The joints that permit motionhave cartilage positioned between the bones providing lubrication to themotion and also absorbing some of the forces direct for the joint. Overtime, the normal use of a joint may wear down the cartilage and bringthe moving bones in a direct contact with each other. In contrast, innormal use, a trauma to a joint, such as the delivery of a large forcefrom an automobile accident for example, may cause considerable damageto the bones, the cartilage or to other connective tissue such astendons or ligaments.

Arthropathy, a term referring to a disease of the joint, is another wayin which a joint may become damaged. One form of joint disease isarthritis, which is generally referred to a disease or inflammation of ajoint that results in pain, swelling, stiffness, instability, and oftendeformity.

There are many different forms of arthritis, with osteoarthritis beingthe most common and resulting from the wear and tear of a cartilagewithin a joint. Another type of arthropathy is osteonecrosis, which iscaused by the death of a part of the bone due to loss of blood supplyand subsequent degeneration of the cartilage. Other types of arthritisare caused by trauma to the joint while others, such as rheumatoidarthritis, Lupus, and psoriatic arthritis destroy cartilage and areassociated with the inflammation of the joint lining.

The hip joint is one of the joints that is commonly afflicted. The hipjoint is a ball and socket joint that joins the femur or thighbone withthe pelvis. The pelvis has a hemispherical socket called the acetabulumfor receiving the head of the femur. Both the head of the femur and theacetabulum are coated with cartilage for allowing the femur toarticulate within the pelvis. Other joints commonly afflicted includethose of the spine, knee, shoulder, elbow, carpals, metacarpals, andphalanges of the hand. One means to address this affliction isarthroplasty which commonly refers to the making of an artificial joint.In severe cases of arthritis or other forms of arthropathy, such as whenpain is overwhelming or when a joint has a limited range of mobility, apartial or total replacement of the joint may be justified. Theprocedure for replacing the joint varies, of course, with the particularjoint in question, but in general involves replacing a terminal portionof an afflicted bone with a prosthetic implant and inserting a memberwith structural support to serve as a substitute for the cartilage.

The prosthetic implant is formed of a rigid material that becomes bondedwith the bone and provides strength and rigidity to the joint and abearing member chosen to allow for lubrication to the joint. Suitablematerials for the implant include metals and composite materials such astitanium, cobalt chromium, stainless steel, ceramic and suitablematerials for the bearing include polyethylene, metal and ceramics. Acement may also be used to secure the prosthetic implant to the hostbone.

Total hip replacement, for example, involves removing the ball shapedhead of the femur and inserting a stemmed implant into the center of thebone, which is referred to as the medullary canal of the bone. The stemimplant may be cemented into the medullary canal or may have a porouscoated surface for allowing the bone to heal directly to the implant.The stemmed implant has a neck and a ball shaped head, which areintended to perform the same functions as the neck and head of a healthyfemur. In some implants, the head is attached to the neck via a taperconnection. It is important to assemble the head to the neck with enoughforce so as to limit micromotion between the head and neck. Theacetabulum of the patient is reamed to receive a shell and liner. Apolyethylene, metal or ceramic liner with a metal shell is inserted intothe acetabulum and acts as socket for receiving the head on the stemmedimplant.

While performing the surgery, it would be beneficial to have aninstrument that can easily and with certainty assemble the head to theneck.

SUMMARY OF THE INVENTION

According to one embodiment of the present invention, an instrument forassembling an implant on a neck is provided. The implant and neck beingcoupled via a taper having a taper axis. The instrument includes a framehaving a distal portion and a proximal portion, the distal portion ofthe frame including a retaining member adapted to engage a portion ofthe neck. The instrument also includes a force applier retained in theproximal portion of the frame. The force applier includes a screw havinga screw axis that is coaxial with the taper axis, wherein the screw isadapted to engage the implant. As the screw is turned, the force applierapplies a force on the implant while the neck is held in place by theframe, thereby causing the tapers of the implant and neck to engage.

According to another embodiment of the present invention, a system forhip orthopaedic surgery is provided. The system includes a neck, animplant, and an instrument. One of the neck and the implant have a maletaper and the other of the neck and the implant have a correspondingfemale taper, wherein when the male and female tapers are engaged, thereis a taper axis. The instrument includes a frame having a distal portionand a proximal portion. The distal portion of the frame includes aretaining member adapted to engage a portion of the neck. The instrumentfurther includes a force applier retained in the proximal portion of theframe, the force applier having an axis that is coaxial with the taperaxis. As the force applier is activated, the force applier applies aforce on the implant while the neck is held stationary by the frame,thereby causing the male and female tapers to engage.

According to yet another embodiment, a method for assembling a taperbetween a neck and an implant is provided. The taper has a taper axis.The method includes using an assembly instrument. The assemblyinstrument includes a frame having a distal portion and a proximalportion. The distal portion of the frame includes a retaining member anda force applier retained in the proximal portion of the frame. The forceapplier has an axis that is coaxial with the taper axis. The methodincludes inserting the neck into the retaining member of the frame andinserting the implant into the proximal portion of the frame. The methodfurther includes applying a force to the implant along the force applieraxis while the retaining member of the frame holds the neck in place,thereby assembling the tapers.

According to yet another embodiment of the present invention, aninstrument for assembling an implant on a neck of a stem is provided.The implant and neck are coupled via a taper having a taper axis. Theinstrument includes a frame having a distal portion and a proximalportion. The distal portion of the frame includes a retaining memberadapted to engage a portion of the neck. The retaining member includes abracket extending from the distal portion of the frame, and the bracketadapted to engage opposing sides of the neck. A force applier is alsoincluded and is retained in the proximal portion of the frame. The forceapplier has an axis that is coaxial with the taper axis. The forceapplier is adapted to engage the implant. As the force applier isactivated, the force applier applies a force on the implant while theneck is held in place by the frame, thereby causing the tapers of theimplant and neck to engage.

According to another embodiment of the present invention, a system forhip orthopaedic surgery is provided. The system includes a stem having aneck, a head, and an instrument. One of the neck and the head have amale taper and the other of the neck and the head have a correspondingfemale taper, wherein when the male and female tapers are engaged, thereis a taper axis. The instrument is adapted to assemble the male andfemale tapers. The instrument includes a frame having a distal portionand a proximal portion. The distal portion of the frame includes aretaining member adapted to engage a portion of the neck, wherein theretaining member includes a bracket extending from the distal portion ofthe frame. The bracket is adapted to engage opposing sides of the neck.The instrument further including a force applier retained in theproximal portion of the frame, having an axis that is coaxial with thetaper axis. The force applier is adapted to engage the implant. As theforce applier is activated, the force applier applies a force on theimplant while the neck is held in place by the frame, thereby causingthe tapers of the implant and neck to engage.

According to another embodiment of the present invention a method forassembling a taper between a neck and an implant is provided. The taperhas a taper axis. The method includes using an assembly instrument,which has a frame having a distal portion and a proximal portion. Thedistal portion of the frame includes a retaining member. The retainingmember includes a bracket extending from the distal portion of theframe. The bracket is adapted to engage opposing sides of the neck. Theinstrument further includes a force applier retained in the proximalportion of the frame, which has an axis that is coaxial with the taperaxis. The method includes inserting the neck into the retaining memberof the frame and inserting the implant into the proximal portion of theframe. The method also includes applying a force to the implant alongthe force applier axis while the frame holds the neck in place, therebyassembling the tapers.

An instrument for assembling a head on a neck of a stem, the implant andneck being coupled via a taper having a taper axis. The instrumentincludes a frame having a distal portion and a proximal portion. Thedistal portion of the frame includes a retaining member adapted toengage a portion of the neck. The retaining member includes a pair ofmoveable arms extending from the distal portion of the frame and thepair of moveable arms adapted to engage a pair of recesses on opposingsides of the neck. The instrument also includes a force applier retainedin the proximal portion of the frame, which has an axis that is coaxialwith the taper axis. The force applier is adapted to engage the implant.As the force applier is activated, the force applier applies a force onthe implant while the neck is held in place by the frame, therebycausing the tapers of the implant and neck to engage.

According to another embodiment, a system for hip orthopaedic surgery isprovided. The system includes a stem having a neck, a head, and aninstrument. The neck has a pair of tool engagement features. One of theneck and the head have a male taper and the other of the neck and thehead have a corresponding female taper, wherein when the male and femaletapers are engaged, there is a taper axis. The instrument is forassembling the male and female tapers, and includes a frame having adistal portion and a proximal portion. The distal portion of the frameincludes a retaining member adapted to engage the tool engagementfeatures of the neck. The retaining member includes a pair of moveablearms, which are adapted to engage the pair of tool engagement features.The instrument further includes a force applier retained in the proximalportion of the frame, and has an axis that is coaxial with the taperaxis. The force applier is adapted to engage the implant, wherein as theforce applier is activated, the force applier applies a force on theimplant while the neck is held in place by the frame, thereby causingthe tapers of the implant and neck to engage.

According to yet another embodiment of the present invention, a methodfor assembling a taper between a neck and an implant is provided. Thetaper has a taper axis. The method includes using an assemblyinstrument, which has a frame having a distal portion and a proximalportion. The distal portion of the frame includes a retaining member.The retaining member includes a pair of moveable arms extending from thedistal portion of the frame. The pair of moveable arms are adapted toengage a pair of recesses on opposing sides of the neck. The instrumentfurther includes a force applier retained in the proximal portion of theframe, which has an axis that is coaxial with the taper axis. The methodalso includes inserting the neck into the retaining member of the frameand inserting the implant into the proximal portion of the frame. Aforce is applied to the implant along the force applier axis while theretaining member of the frame holds the neck in place, therebyassembling the tapers.

According to anther embodiment of the present invention, an instrumentfor assembling an implant on a neck of a stem is provided. The stem hasa stem axis and the implant and neck being coupled via a taper having ataper axis. The instrument includes a frame having a distal portion, amiddle portion having a body axis that is coaxial with the stem axis,and a proximal portion. The distal portion of the frame includes aretaining member adapted to engage a portion of the neck and a connectoradapted to engage a corresponding feature of the stem. The instrumentalso includes a force applier retained in the proximal portion of theframe and having an axis that is coaxial with the taper axis. The forceapplier is adapted to engage the implant. The force applier axis is notcoaxial or parallel with the stem access. As the force applier isactivated, the force applier applies a force on the implant while theneck is held in place by the frame, thereby causing the tapers of theimplant and neck to engage.

According to yet another embodiment of the invention, a system for hiporthopaedic surgery is provided. They system includes a stem having aneck, a head, and an instrument. One of the neck and the head have amale taper and the other of the neck and the head have a correspondingfemale taper. When the male and female tapers are engaged, there is ataper axis. The instrument is for assembling the tapers and includes aframe having a distal portion and a proximal portion and a body axis.The distal portion of the frame includes a retaining member adapted toengage a portion of the neck. The instrument further includes a forceapplier retained in the proximal portion of the frame and has an axisthat is coaxial with the taper axis but that is not coaxial or parallelwith the stem axis. The force applier is adapted to engage the implant,and as the force applier is activated, the force applier applies a forceon the implant while the neck is held in place by the frame, therebycausing the tapers of the implant and neck to engage.

According to yet another embodiment of the present invention, a methodfor assembling a taper between a neck of a stem and an implant isprovided. The taper has a taper axis and the stem having a stem axis.The method includes using an assembly instrument, which has a framehaving a distal portion, proximal portion, and a middle portion having abody axis. The distal portion of the frame includes a retaining member.The instrument having a force applier, which has an axis that is coaxialwith the taper axis, wherein the force applier axis is not coaxial orparallel with the stem axis. The neck is inserted into the retainingmember of the frame and the implant is inserted into the proximalportion of the frame. A force is applied to the implant along the forceapplier axis while the retaining member of the frame holds the neck inplace, thereby assembling the tapers.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 is a perspective view of a first embodiment of an assembly tool,shown as it may be used for assembling a head component and a stemcomponent of a hip replacement prosthesis;

FIG. 2 is a front view of the assembly tool of FIG. 1, shown as it maybe used for assembling the head and stem components;

FIG. 3 is a perspective view of a second embodiment of the assemblytool, shown as it may be used for assembling the head and stemcomponents, while the stem is positioned in the femur of a surgicalpatient;

FIG. 4 is a detailed, internal view of a portion of the assembly toolshown in FIG. 3, showing a quick release mechanism;

FIG. 5 is a perspective view of a third embodiment of the assembly tool,shown as it may be used for assembling the head and stem components,while the stem is positioned in the femur of a surgical patient;

FIG. 6 is a detailed, partial, sectional view of the assembly tool shownin FIG. 5, showing how a pair of opposing arms may be drawn togetherabout the stem component;

FIG. 7 is a perspective view of a fourth embodiment of the assemblytool, shown as it may be used for assembling the head and stemcomponents, while the stem is positioned in the proximal femur of asurgical patient;

FIG. 8 is a perspective view of a fifth embodiment of the assembly tool,shown as it may be used for assembling an intermediate component and astem component of a hip replacement prosthesis, showing only theproximal portion of the stem component;

FIG. 9 is a sectional view of a portion of the assembly tool shown inFIG. 8, showing the intermediate component assembled onto a taper of thestem component, and a first embodiment of a protective insert; and

FIG. 10 is a sectional view of a portion of the assembly tool shown inFIG. 8, showing the head component assembled onto the taper of the stemcomponent, and a second embodiment of the protective insert.

FIG. 11 is a perspective view of a sixth embodiment of the assemblytool.

DETAILED DESCRIPTION

Any one of the assembly tool embodiments next described may be usedduring a surgical, hip replacement procedure to assemble a headcomponent to a stem component of a hip replacement prosthesis that isimplanted in the proximal femur of a surgical patient. Each of thefigures show at least partial views of a hip replacement prosthesis 30,which has a head 2 and a stem 6 that defines a stem axis 18. During ahip replacement surgical procedure, the surgeon implants the distalportion of stem 6 into the intramedullary canal of the proximal femur ofthe surgical patient. The proximal part of stem 6 includes a neck 8having a taper 10 that defines a taper axis 20, which is normallyoriented relative to stem axis 18 at an angle of about 135 degrees,although this angle may vary. Head 2 includes a taper recess 4 forassembly to taper 10, and the taper design may be a Morse taper oranother taper design variation. Head 2 may be spherical or nearlyspherical and may be formed from a metal such as, for example, a cobaltchromium alloy, or from a ceramic such as, for example, an aluminumoxide. The size, material, configuration, and surface treatment of eachof head 2 and stem 6 depend on the patient anatomy and condition, typeof hip replacement prosthesis used (primary or revision), surgicalpreferences, and other factors. Stem 6 may be formed from a metal suchas, for example, a stainless steel or a titanium alloy. Stem 6 may alsoinclude a threaded bore 16 (FIG. 2) located in the proximal portion ofstem 6 and coaxial with stem axis 18. Threaded bore 16 may be providedfor use with conventional, insertion and/or extraction instruments, butmay also be used for attachment of the assembly tool, as will bedescribed.

For some types of hip replacement prostheses, an intermediate componentmay be assembled between the head and the stem, for example, to providea desired offset from the taper axis. Hip replacement prosthesis 30 ofFIG. 8 shows an example of such an intermediate component, an offsetcomponent 14 that has both a taper 24 for assembly to head 2 and a taperrecess 34 for assembly to stem 6. Each of the assembly tool embodimentsherein may easily be adapted for assembling either one of theintermediate component or the head component to the stem component.Another type of intermediate component is a sleeve without an offsetfeature. A sleeve would also have both a taper for assembly to the head2 and a tapered recess for assembly to the neck 8 of the stem 6. Thesetypes of sleeves are well known in the art.

A user, such as a surgeon or a surgical assistant, may use any one ofthe assembly tool embodiments next described to apply controllably asufficient, quasistatic axial force to join the head component to thestem component. A quasistatic axial force shall be understood to be anaxial force that is applied gradually, increasing from a low to a high,peak magnitude. Conversely, a quasidynamic axial force shall beunderstood to be a high axial force that is applied, more or less,instantaneously, such as like a hammer strike.

For each of the following embodiments, the assembly tool generallyincludes a frame and a force applier. The frame has a proximal portionthat supports the force applier for controllably applying a quasistaticforce of a desired magnitude to the proximal side of the head, in adirection that is coaxial with taper axis 20. The frame also has adistal portion that removably engages or connects to a proximal part ofthe stem, thereby providing an opposing, retention force distal to thetaper connection, such that substantially no axial force is transmittedto the femur during actuation of the force applier. The assembly toolmay be hand operable and can provide at least a peak axial force ofabout 4 kN. Briefly, the user first hand assembles the head and stemcomponents, then positions and engages the assembly tool onto the headand stem components, and then actuates the assembly tool to complete theassembly of the head and stem components. Once the user has assembledthe head and stem components, the user may reversely actuate the forceapplier and remove the assembly tool from the surgical site.

FIG. 1 is a perspective view and FIG. 2 is a front view of a firstembodiment of an assembly tool 100, shown as it may be used forassembling together head 2 and a stem 6 of hip replacement prosthesis30. Assembly tool 100 has a frame 150 with a proximal portion 106supporting a force applier 152, and a distal portion 104 that isremovably attachable to the proximal part of stem 6. Frame 150 isconfigured such that actuation of force applier 152 provides aquasistatic, axial force along taper axis 20 to the proximal side ofhead 2, and distal portion 104 provides an opposing, retaining forcedistal to taper 10 of stem 6, such that substantially no axial forcegenerated by force applier 152 is transmitted to the femur.

A retaining member having a bracket 114 extends from body element 140 inthe distal portion 106 of frame 150. Bracket 114 is U-shaped and retainsa protective insert 136 that wraps around the opposing sides of neck 8of stem 6 to stabilize and maintain alignment of frame 150 on stem 6during actuation of force applier 152.

Force applier 152 has an adjustable screw 108 that defines a screw axis120 (also referred to as a force applier axis), an actuator 110 forturning screw 108 about force applier axis 120, which is coaxial withtaper axis 20, and a foot 112 attached to the distal end of screw 108for engaging head component 2 of hip replacement prosthesis 30. Proximalportion 104 of frame 150 has an internally threaded throughbore thatthreadably retains screw 108, such that rotation of screw 108 aboutscrew axis 120 in a first direction advances screw 108 towards head 2along taper axis 20, and rotation of screw 108 about screw axis 120 in asecond direction moves screw 108 away from head 2. Frame 150 also has amiddle portion 102 between proximal and distal portions 104, 106. Middleportion 102 has an elongate body 140 defining a body axis 138, which iscoaxial with stem axis 18 when frame 150 is attached to stem 6. Bodyelement 140 is hollow and retains a connector, such as a threaded bolt116 (hidden) that may be threadably inserted into threaded bore 16 ofstem 6. The user may rotate, about body axis 138, a bolt knob 118connected to the proximal end of threaded bolt 116 for threadable andremovable attachment of frame 150 to stem 6.

Middle portion 102 also has a carriage 126 that is retained on andadjustably positionable on body 140 in a first direction, as indicatedby arrow A. Carriage 126 slidably retains proximal portion 106, which isadjustably positionable on carriage 126 in a second direction that isperpendicular to the first direction, as indicated by arrow B. Carriage126 has a first screw clamp 128 and a second screw clamp 130 that may beloosened by the user to allow adjustment of proximal portion 106 in thefirst and second directions, respectively, to align foot 112 and screwaxis 120 of force applier 152 with taper axis 20. Once aligned, the usermay tighten first and second screw clamps 128, 130 to fix the positionof proximal portion 106.

A universal swivel joint 124 bipivotably attaches actuator 110 to screw108. Actuator 110 is sized and shaped for gripping by the user forapplying sufficient torque to screw 108 to achieve the desired, peakaxial force.

Foot 112 may be formed from a non-metallic material such as a polymer oran elastomer to prevent damage to head 2. Foot 112 may be rotatablyattached to the end of screw 108 such that upon reaching a certainapplied axial force, screw 108 turns about screw axis 120 in foot 112.Alternately, foot 112 may be fixedly attached to the end of screw 108,such that foot 112 and screw 108 always rotate together about screw axis108 during actuation of force applier 152.

FIG. 3 is a perspective view of a second embodiment, assembly tool 200,shown as it may be used for assembling head 2 onto stem 6 while stem 6is positioned in the femur. Assembly tool 200 has a frame 250 with aproximal portion 206 supporting a force applier 252, and a distalportion 204 that is removably attachable to threaded bore 16 (see FIG.2) of stem 6 using a bolt 216. The force applier 252 may be adjustableto implant various head sizes and offsets. Frame 250 is configured suchthat actuation of force applier 252 provides a quasistatic, axial forcealong taper axis 20 to the proximal side of head 2, and distal portion204 provides an opposing, retaining force distal to taper 10 of stem 6,such that substantially no axial force generated by force applier 252 istransmitted to the femur.

Frame 250 also has a middle portion 202 between proximal portion 206 anddistal portion 204. Middle portion 202 has a body 240 defining a bodyaxis 238. Body 240 slidably retains proximal portion 206 for movementbetween a first position (shown in FIG. 4) and a second position (shownin FIG. 3). A hand grip 244 extends from the proximal end of bodyelement 240 along body axis 238. A quick-release actuator 242 pivotablyattaches to the proximal end of body element 240, such that the user mayoperate it using the same hand that is holding hand grip 244. A linkage246, shown in FIG. 4, operationally connects quick-release actuator 242to proximal portion 206. In the second position, linkage 246 is in alocked orientation so that actuation of force applier 252 does not moveproximal portion 206 away from head 2.

Proximal portion 206 has a threaded throughbore (hidden) and threadablyretains a screw 208 that defines a screw axis 220. A foot 212 isattached to the distal end of screw 208 and is similar to foot 112 ofassembly tool 100. An actuator 210 is a hex-drive screw head and may bedriven by a conventional, surgical, hex-drive tool (not shown) to rotatescrew 208 about screw axis 220 in a first direction to move foot 212along screw axis 220 and towards head 2, and in a second direction tomove foot 212 along screw axis 220 and away from head 2. The hex-drivetool may be a torque-limiting tool so that the desired, peak axial forcemay not be exceeded.

A retaining member includes a bracket 214 with a protective insert 236extends from distal portion 204 and is U-shaped to wrap around the sidesof neck 8 of stem 6 to help stabilize and maintain alignment of frame250 during actuation of force applier 252.

FIG. 5 is a perspective, partial view of a third embodiment, assemblytool 300, shown as it may be used for assembling head 2 and stem 6 afterstem 6 has been inserted into the proximal femur. Assembly tool 300 issimilar to assembly tool 200 of FIG. 3, differing only by the attachmentmeans to stem 6.

Assembly tool 300 has a frame 350 with a proximal portion 306, a distalportion 304, and a middle portion 302. Proximal portion 306 threadablyretains a force applier 352, which has a screw 308 that defines a screwaxis 320, a foot 312, and an actuator 310 (partially shown). Screw axis320 is coaxial with taper axis 20. Middle portion 302 has a body 340that defines a body axis 338, which is spaced apart from and parallel toscrew axis 320. Body 340 slideably retains proximal portion 306, whichis adjustably positionable on body element 340 between a first and asecond position, as indicated by arrow E.

Distal portion 304 has a retaining member having a slot 318 that retainsa first arm 314 and an opposing, second arm 316, each of which extendperpendicularly from body axis 338. Each of arms 314, 316 is pivotablyattached to distal portion 304, such that arms 314, 316 can swingindependently of each other within the same plane as shown in FIG. 6.Distal portion 304 threadably retains a locking screw 348, which definesa lock screw axis 346 and which is oriented with respect to arms 314,316, such that when screw 348 is advanced along screw axis 346, the tip(which may be conically shaped) of screw 348 drives between arms 314,316 to draw arms 314, 316 together. Conversely, loosening screw 348 inthe opposite direction allows arms 314, 316 to open.

Assembly tool 300 may only be used with a stem component havingcompatible, tool engagement features. A first engagement recess 54 and asecond engagement recess 56 are located on opposing sides of a neck 48of a modified, stem 46, such that taper axis 20 extends approximatelybetween them. First and second engagement recesses, 54, 56, may beformed into stem 46 to a relatively shallow depth, for example 1-3 mm,and have any one of a number of possible profiles, such as, for example,rectangular, circular, or D-shape. Each of a first tip 324 of arm 314and a second tip 326 of second arm 316 may be configured to fit snugglywithin either of recesses 54, 56 of stem 6. To attach frame 350 to stem46, the user positions tips 324, 326 of arms 314, 316 over recesses 54,56, of neck 48, respectively, when arms 314, 316 are open, whilecentering foot 312 over head 2. The user then tightens arms 314, 316using a conventional drive tool to advance screw 348 along screw axis346, so that tips 324, 326 tightly clamp into recesses 54, 56, therebyforming a rigid connection between frame 350 and stem 46. The user maythen position foot 312 onto head 2 and actuate force applier 352 tocomplete the assembly of head 2 to stem 46. The user may grip frame 350with one hand to stabilize it while using the other hand to actuateforce applier 352.

FIG. 7 is a perspective view of a fourth embodiment, assembly tool 400,shown as it may be used for assembling head 2 onto stem 46 while stem 46is positioned in the proximal femur. Assembly tool 400 has a frame 450with a proximal portion 406, a middle portion 402, and a distal portion404. Proximal portion 406 retains a force applier 452, which has a screw408 defining a screw axis 420, a foot 412, and an actuator 410. Proximalportion 406 has a body 440 with an internally threaded bore thatthreadably retains screw 408. Body 440 defines a body axis 438. Bothbody axis 438 and screw axis 420 are coaxial with taper axis 20. Theuser may grip and turn actuator 410 in a first rotational directionabout screw axis 420 to advance screw 408 towards head 2, and in theopposite, second rotational direction to move screw 408 away from head2.

Body 440 has a first channel 442 that slidably retains a first elongatearm 456 defining a first arm axis 468. Body 440 also has a secondchannel 444 that slidably retains a second elongate arm 458 defining asecond arm axis 470. First and second arm axis 468, 470 are parallel tobody axis 420. The proximal ends (analogous to a person's “shoulders”)of first and second elongate arms 456, 458 are mounted on opposing sidesof body 440. First elongate arm 456 is positionable in a directionperpendicular to body axis 438, as indicated by arrow F. Second elongatearm 458 is positionable in a direction perpendicular to body axis 438,as indicated by arrow E. A first screw clamp 448 and a second screwclamp 446 allow the user to independently position and fix each of firstand second elongate arms, 456, 458, respectively, at a desired, spacedapart position, relative to body axis 438.

Assembly tool 400 may only be used with a stem component havingcompatible, tool engagement features, such as described for assemblytool 300. First and second recesses, 54, 56 of stem 46 may be employedas anchoring locations for the distal ends (analogous to “hands”), offirst and second elongate arms 456, 458. The user may assemble head 2onto stem 46 in a manner similar to that described for assembly tool300.

FIG. 8 is a perspective view and FIG. 9 is a partial view of a fifthembodiment, assembly tool 500, shown as it may be used for assemblingintermediate component 14 (shown in a sectional view) onto stem 6 of hipreplacement prosthesis 30 (showing only the proximal portion). Assemblytool 500 has a frame 550 with a proximal portion 506, a middle portion502, and a distal portion 504. Proximal portion 506 retains a forceapplier 552 having a screw 508 defining a screw axis 520, an actuator510, and a foot 512. Middle portion has a body 540 that has a first arm522 and a second arm 524, each of which is fixed and equally spacedapart from a body axis 538. Screw axis 520 and body axis 538 are coaxialwith taper axis 20. Distal portion 504 has a retaining member, which inthis embodiment is a semicircular, annular groove 544 that retains afirst embodiment, protective insert 536. Frame 550 is rigid andconfigured (like half of an “open clamshell”) to allow positioning ofassembly tool 500 onto hand-assembled, offset component 14 and neck 8 ofstem 6, even if stem 6 has already been fully inserted into the proximalfemur. Protective insert 536 is sized and shaped to conform to a neckcontour 40 that is immediately distal to taper 10 of neck 8. Protectiveinsert 536 may be formed from a non-metallic, biocompatible,sterilizable material, such as PEEK, UHMWPE, polycarbonate, or any of anumber of available, engineering plastics. The user may use assemblytool 500 in a very similar manner as previously described for the otherembodiments.

FIG. 10 is a partial view of assembly tool 500, shown as it may be usedfor assembling head 2 (shown in a sectional view) onto stem 6 (showingonly the proximal portion). Assembly tool 500 is shown with a secondembodiment, protective insert 566, which is configured to extendpartially into taper recess 4 of head 2. Protective insert 566 providesfor situations in which taper 10 is shorter than taper recess 4, andupon assembly, head 2 “hangs” over neck 8 a small distance.

FIG. 11 is a perspective view of a sixth embodiment, an assembly tool600, as a surgeon may position it to assemble head 2 onto stem 6.Similar to the previous embodiments, assembly tool 600 has a frame 650that is removably attachable to stem 6, and a force applier 652 for thecontrollable application of a clamping force to head 2 along taper axis20. Force applier 652 has an elongate screw 608 defining a screw axis620, an actuator 610 attached to the proximal end of screw 608, and afoot 612 attached to the distal end of screw 608.

Frame 650 has a distal portion 604, a middle portion 602, and a proximalportion 606. Distal portion 604 has a connector 616 for the removableattachment of frame 650 to stem 6. As previously described for assemblytool 100 (FIG. 1), the proximal body of stem 6 may be provided with athreaded bore, coaxial with stem axis 16, for the attachment of aninsertion and/or extraction instrument. If stem 6 is provided with sucha threaded bore, connector 616 may be a threaded bolt inserted through acounterbored through-hole 630 in distal portion 604. Counterboredthrough-hole 630 defines a hole axis 624. During the surgical procedure,the surgeon may use a conventional driver to tighten connector 616 whenattaching frame 650 to stem 6, and to loosen connector 616 when removingframe 650 from stem 6. However, those skilled in the art will appreciatethat connector 616 may be any one of numerous types of mechanicalelements/mechanisms adapted to removably attach to any one of numeroustypes of slots, recesses, undercut holes, and the like, that may beprovided in the proximal stem body, either specifically for use withassembly tool 600 or for alternate purposes, such as for the insertionand/or an extraction of the stem. For each of these arrangements, thesurgeon may use connector 616 to achieve a secure, removable attachmentof frame 650 to stem 6, in order to provide a retention force thatopposes the applied clamping force, thereby minimizing the transfer offorce to the femur during actuation of force applier 652.

Distal portion 604 of frame 650 also includes a bracket 614 that helpsto maintain the correct alignment of frame 650 with respect to taperaxis 20 during the application of the clamping force using force applier652. As described for assembly tool 100 (FIG. 1), bracket 614 may beprovided with a protective insert 636 that helps prevent damage to thesurface of the neck of stem 6. Bracket 614 is U-shaped for easypositioning around the neck of stem 6 prior to attaching connector 616to stem 6, and for removal of assembly tool 600 from stem 6 afterassembly of head 2 onto stem 6.

Proximal portion 606 of frame 650 has a body 640 defining a body axis638. Body 640 is generally tubular and has an internal screw thread(hidden in FIG. 12) extending at least along a portion of the length ofbody 640. Body 640 threadably retains screw 608 of force applier 652,such that screw axis 620 is coaxial with taper axis 20 when assemblytool 600 is properly positioned for actuation of force applier 652.

To actuate force applier 652, the surgeon rotates actuator 610 in afirst direction (i.e., clockwise) to move foot 612 along taper axis 20and towards head 2. Conversely, to deactuate force applier 652, thesurgeon rotates actuator 610 in a second direction (i.e.,counterclockwise) to loosen and remove force applier 652 from head 2.Actuator 610 may have a T-bar configuration as shown in FIG. 12. Thesize and shape of actuator 610 may be based on ergonometric data knownin the art, so that a person with average hand/arm strength could easilyapply the necessary torque to achieve at least a predetermined, desiredclamping force. Alternatively, actuator 610 may be provided with atorque-limiting mechanism, of which numerous types are well-known in themechanical, hand tool industry, such that it would be impossible for thesurgeon to apply a clamping force that exceeds the predetermined,desired force. The actual magnitude of the predetermined, desired forcemay be recommended by the implant manufacturer, and be based on theappropriate testing and analysis of the taper connection.

Proximal portion 604 and middle portion 602 of frame 650 define an armaxis 624 that is parallel and offset from screw axis 620. As shown inFIG. 12, middle portion 602 may be configured to be slidably retained ina channel 642 of body 640. The surgeon may loosen a screw clamp 646 toadjust the offset of arm axis 624 relative to screw axis 620, such asmay be desirable for different sizes and configurations of stem and headcomponents. The surgeon may then tighten screw clamp 646 to maintain arigid attachment of middle portion 602 to body 640. This ability toseparate proximal portion 606 from middle portion 602 also may beadvantageous for cleaning/sterilizing assembly tool 600 or for moreefficiently storing assembly tool 600 in a surgical tray. Alternatively,middle portion 602 may be fixedly attached to body 640, in which casefoot 612 may be designed to accommodate various stem configurations andhead sizes. In the latter arrangement, for example, foot 612 may berigidly attached to screw 608 and have a flat face for interfacingagainst head 2, thereby allowing slight misalignment of screw axis 620and taper axis 20.

Each component of assembly tool 600 may be formed from any one ofnumerous types of stainless steels or biocompatible polymers commonlyused for multiple-use and single-use, surgical instruments. Protectiveinsert 636 and foot 612 may be formed from a biocompatible polymer, forexample PEEK, which is softer than the implant materials, in order toprevent damage to the implant surfaces. Protective insert 636 may alsobe formed from a biocompatible elastomer, such as silicone rubber, thatis retained on or bonded to bracket 614.

As those skilled in the art will appreciate, there are many variationsof the assembly tool embodiments described herein. For example, any ofthem may have an actuator that incorporates a force limiting mechanismto prevent applying excessive torque while actuating the force applier.Also, any of them may have one or more additional grips or handlesextending from or incorporated into the assembly tool frame to helpmaintain stability and alignment of the assembly tool while actuatingthe force applier. Also, each of the assembly tool embodiments may bedesigned to be either one of a single-use (disposable) or a multiple-use(reusable) device. Also, in addition to mechanical, screw-driven typesof force appliers, other types of force appliers may include, forexample, the following: mechanical, ratcheting types; hydraulicallydriven types; pneumatically driven types; expanding gas-driven types(incorporating, for example, a small, disposable canister of carbondioxide gas); electrical, motor-driven gear mechanism types; andmechanical, linkage driven types. An assembly tool having any one ofthese types of force appliers can provide the user with the ability tocontrollably apply a quasistatic, axial force that has the desired, peakmagnitude (such as about 1000 pounds/5000 N) and that is directed alongthe taper axis of the head and stem components to fully join thosecomponents.

What is claimed is:
 1. An instrument for assembling an implant on a neckof a stem, the implant and neck being coupled via a taper having a taperaxis, the instrument comprising: a frame having a distal portion and aproximal portion, the distal portion of the frame including a retainingmember adapted to engage a portion of the neck, wherein the retainingmember includes a bracket extending from the distal portion of theframe, the bracket adapted to engage opposing sides of the neck; a forceapplier retained in the proximal portion of the frame, having an axisthat is coaxial with the taper axis, wherein the force applier isadapted to engage the implant; wherein as the force applier isactivated, the force applier applies a force on the implant while theneck is held in place by the frame, thereby causing the tapers of theimplant and neck to engage.
 2. The instrument of claim 1, wherein theforce applier is a screw and an actuator coupled to the screw, whereinthe actuator is adapted to enable a user to turn the screw.
 3. Theinstrument of claim 1, wherein at least a portion of the frame isadjustable along a longitudinal axis.
 4. The instrument of claim 1,wherein the proximal portion further includes a foot coupled to theforce applier and the implant, such that as the force applier isactivated, the foot engages the implant.
 5. The instrument of claim 1,wherein the distal portion of the frame further includes a threaded boltadapted to engage a threaded bore on the stem.
 6. The instrument ofclaim 1, wherein the bracket includes a protective insert to stabilizeand maintain alignment of the frame.
 7. A system for hip orthopaedicsurgery comprising: a stem having a neck; a head, wherein one of theneck and the head have a male taper and the other of the neck and thehead have a corresponding female taper, wherein when the male and femaletapers are engaged, there is a taper axis; and an instrument forassembling the male and female tapers, the instrument including a framehaving a distal portion and a proximal portion, the distal portion ofthe frame including a retaining member adapted to engage a portion ofthe neck, wherein the retaining member includes a bracket extending fromthe distal portion of the frame, the bracket adapted to engage opposingsides of the neck, the instrument further including a force applierretained in the proximal portion of the frame, having an axis that iscoaxial with the taper axis, wherein the force applier is adapted toengage the implant, wherein as the force applier is activated, the forceapplier applies a force on the implant while the neck is held in placeby the frame, thereby causing the tapers of the implant and neck toengage.
 8. The instrument of claim 7, wherein the force applier is ascrew and an actuator coupled to the screw, wherein the actuator isadapted to enable a user to turn the screw.
 9. The instrument of claim7, wherein at least a portion of the frame is adjustable along alongitudinal axis.
 10. The instrument of claim 7, wherein the proximalportion further includes a foot coupled to the force applier and thehead, such that as the force applier is activated, the foot engages thehead.
 11. The instrument of claim 7, wherein the distal portion of theframe further includes a threaded bolt adapted to engage a threaded boreon the stem.
 12. The instrument of claim 7, wherein the bracket includesa protective insert to stabilize and maintain alignment of the frame.13. A method for assembling a taper between a neck and an implant, thetaper having a taper axis, the method comprising: using an assemblyinstrument, the assembly instrument including a frame having a distalportion and a proximal portion, the distal portion of the frameincluding a retaining member, wherein the retaining member includes abracket extending from the distal portion of the frame, the bracketadapted to engage opposing sides of the neck, the instrument furtherincluding a force applier retained in the proximal portion of the frame,the force applier having an axis that is coaxial with the taper axis;inserting the neck into the retaining member of the frame; inserting theimplant into the proximal portion of the frame; and applying a force tothe implant along the force applier axis while the frame holds the neckin place, thereby assembling the tapers.
 14. The method of claim 13,wherein the force applier is a screw and an actuator coupled to thescrew, wherein the actuator is adapted to enable a user to turn thescrew.
 15. The method of claim 13, wherein at least a portion of theframe is adjustable along a longitudinal axis.
 16. The method of claim13, wherein the proximal portion further includes a foot coupled to theforce applier and the head, such that as the force applier is activated,the foot engages the head.